OPTIMIZATION OF ASA EMULSIFICATION IN INTERNAL SIZING OF PAPER AND BOARD potx

HELSINKI UNIVERSITY OF TECHNOLOGY
Faculty of Chemistry and Materials Sciences
Degree Programme of Forest Products Technology




Jarno-Petteri Merisalo


OPTIMIZATION OF ASA EMULSIFICATION IN
INTERNAL SIZING OF PAPER AND BOARD


Thesis for the degree of Master of Science in Technology submitted for inspection,
Espoo November 13, 2009.



Supervisor Professor Janne Laine


Instructor Juha Lindfors, D.Sc.(Tech.)





HELSINKI UNIVERSITY OF TECHNOLOGY
Faculty of Chemistry and Materials Sciences
Degree Programme: Forest Products Technology

ABSTRACT OF MASTER’S THESIS
Author
Jarno-Petteri Merisalo
Title of Thesis
Optimization of ASA emulsification in internal sizing of paper and board
Abstract
In paper- and boardmaking, internal sizing is used for making the end product more resistant to liquid penetration. Rosin, Alkyl Ketene
Dimer (AKD) and Alkenyl Succinic Anhydride (ASA) internal sizing agents exist for this purpose. ASA is added to the papermaking
process in the form of an emulsion. The dispersion of ASA oil, water, and a stabilizing agent (stabilizer) are mixed under shear forces to
create the emulsion.
In this master’s thesis, different emulsions, emulsification techniques and stabilizers in the process industry were studied. Emulsions in
food, medical, petroleum and papermaking processes had potential stabilizers to be used for hydrophobation of paper and board with
ASA. The comparison between rosin, AKD and ASA internal sizing agents was also done. The goal was to find optimal emulsification
methods and emulsion stabilizers for ASA emulsification.
The effect of different ASA compounds, one pure ASA and the other, easy emulsifying (EE-ASA), with surface active agents (surfactants)
added, were examined with various emulsion stabilizers. Emulsification process of ASA was studied by choosing thirty four stabilizers
based on earlier experiments and literature over various fields of emulsification. The chosen stabilizers were reference cationic potato
starch, different charge densities and molecular weights having cationic and anionic polyacrylamides (C- and A-PAM's), caboxymethyl
celluloses (cmc's) and amphoteric polymers, among other stabilizers which gave steric or electrostatic stabilization effect on emulsion
droplets. For the nano- and microparticle stabilization effect, bentonite and colloidal silica were utilized. Particle size, pH and visual de-
terminations were carried out and twenty stabilizers were selected for turbidity and zeta potential testing. A good ASA emulsion particle
size was in between 0.5 µm – 5 µm in d(0.5) values. The most stable emulsions had no phase inversion, only little creaming and foaming
during the 4 hour study.
Eleven stabilizers were selected for sheet tests with ASA dosages of 1 kg/t and 2 kg/t. Water absorption tests showed the highest hydro-
phobation with medium molecular weight and medium charge density having 6.C-PAM and pure ASA and with polyvinyl alcohol, PVA
3-96, with both ASA's. Generally, pure ASA produced higher hydrophobation with only little difference to EE-ASA. The best Cobb
60

hydrophobation values were around 21-23 g/m² of absorbed water. The best dry tensile index, around 90 Nm/g, were seen with cationic
starch and EE-ASA, and the best wet tensile index of 65 Nm/g with medium molecular weight, medium cationic polyamidoamine-

epichlorohydrin (PAAE) and EE-ASA.
Finally, six stabilizers were selected for deposition tests where ASA emulsions were exposed to precipitated calcium carbonate (PCC),
CaCO
3
, which is known to forms sticky deposits with ASA's hydrolysis products in paper or board machines water circulation. ASA
emulsions stabilized with reference cationic starch showed the lowest deposit amounts, 1.3 and 1.2 g/m², with pure ASA and with EE-
ASA. With EE-ASA, medium molecular weight and medium charge density having 6.C-PAM gained value 5.4 g/m² but caused serious
deposition problems with pure ASA. The deposit nature on sample steel plates varied. PAAE emulsion was easy to remove from the metal
surface, whereas starch emulsion would have needed chemical treatment to be removed. PAAE with pure ASA, indicated below average
deposition amounts, 11.5 g/m². Generally neither of the two ASA's was superior compared to the other, when considering fouling. Refer-
ence starch and PVA indicated smallest ASA amounts on the deposition test sample plates based on thermal gravimetric analysis.
Cost savings could be realized with 6.C-PAM and with PAAE stabilizers with both ASA's. For reference starch, there was practically no
difference between the two ASA's and for the 6.C-PAM, EE-ASA was better, whereas for PAAE, pure ASA showed best total results. The
PAAE positive effects to wet strength made the chemical commercially interesting.
Supervisor Instructor
Janne Laine, Prof. Juha Lindfors, D.Sc.(Tech.)
Chair Chair code
Forest Products Chemistry Puu-19
Pages Language
100 + 8 English
Keywords Date
Emulsion, emulsification, ASA, internal sizing, paper 11/13/2009




TEKNILLINEN KORKEAKOULU
Kemian ja materiaalitieteiden tiedekunta
Koulutus-/tutkinto-ohjelma: Puunjalostustekniikka
DIPLOMITYÖN TIIVISTELMÄ

Tekijä
Jarno-Petteri Merisalo
Diplomityön nimi
Alkenyyli meripihkahappoanhydridin emulgoinnin optimointi paperin ja kartongin massaliimauksessa
Tiivistelmä
Diplomityön tavoitteena oli löytää paperin ja kartonginvalmistukseen sopivia emulsiota stabiloivia kemikaaleja eri teollisuudenalojen
kirjallisuudesta. Kiinnostavimmat stabilointiaineet valittiin käytettäväksi alkenyyli meripihkahappoanhydridin (ASA) massaliimaemulsion
valmistamiseen. Massaliimareseptin optimoinnin tavoitteena oli tuottaa mahdollisimman stabiili massaliimaemulsio, joka liimaa hyvin
paperia ja kartonkia, toimii paperi- ja kartonkikoneella likaamatta prosessia, sekä mahdollistaa kustannustehokkaan hinnan asiakkaalle
matalan annostarpeen myötä, lisäten paperin- ja kartonginvalmistuksen taloudellista kannattavuutta.
Kirjallisuusosassa vertailtiin eri teollisuuden alojen emulsioita (esimerkiksi ruoka-, lääke-, öljy-, ja paperiteollisuuden kemikaalit) ja niissä
käytettyjä emulsion stabilointiaineita ja -menetelmiä. Tarkemmin vertailtiin paperin ja kartongin massaliimauksessa yleisesti käytettyjä
ASA, alkyyli keteeni dimeeri (AKD) ja hartsiliimoja. ASA:n emulgointikokeita varten tutkittiin erilaisia steerisesti ja elektrostaattisesti
emulsiota stabiloivia stabilointiaineita. Referenssiaineeksi valittiin yleisesti käytetty kationinen perunatärkkelys. Lisäksi stabilointiaineina
käytettiin muun muassa eri varaustiheydellä ja molekyylipainoilla olevia kationisia ja anionisia polyakryyliamideja (C- ja A-PAM), amfo-
teerisia polymeereja ja karboksyylimetyyliselluloosia (CMC). Emulsion stabilointiin nano- ja mikropartikkeleilla valittiin bentoniitti ja
silika. Kokeissa käytettiin kahta erilaista ASA:a. Ensimmäinen oli puhdas ASA yhdiste ja jälkimmäisessä, EE-ASA:ssa, oli mukana pinta-
aktiivisia aineita, tavoitteenaan helpottaa emulgointiprosessia.
Emulgoitiin 34 stabilointiainetta kummankin ASA:n kanssa ja määritettiin emulsioista pH, partikkelikoko sekä visuaaliset ominaisuudet.
Kaksikymmentä kiinnostavinta stabilointiainetta jatkoivat zeta potentiaali ja turbiditeetti mittauksiin. Emulsiopisaroiden tavoitekoko oli
välillä 0,5-5 µm d(0,5) arvoina. Lisäksi tavoitteena oli, ettei kermoittumista, sedimentoitumista tai vaahtoamista neljän tunnin seuranta-
ajanjaksona juurikaan esiintyisi. Yksitoista stabilointiainetta valittiin arkkikokeisiin, joissa käytetyt ASA-annokset olivat 1 kg/t ja 2 kg/t.
Korkeimmat paperin hydrofobisuusarvot saavutettiin keskimolekyylipainoisella ja keskivaraustiheyksisellä 6.C-PAM:illa ja puhtaalla
ASA:lla, polyvinyyli alkoholilla (PVA), ja EE-ASA:lla, sekä referenssitärkkelyksellä kummallakin ASA-liimalla. Puhtaan ASA:n havait-
tiin tuottavan hieman korkeampaa hydrofobisuutta kuin EE-ASA. Parhaat paperin hydrofobointiarvot olivat 21-23 g/m² paperiin absorboi-
tunutta vettä. Paras kuivavetoindeksi saavutettiin kationisella tärkkelyksellä, noin 90 Nm/g ja EE-ASA:lla, paras märkävetoindeksi saavu-
tettiin keskimolekyylipainoisella, keskikationisella polyamidiamiini-epiklorohydriinillä (PAAE) ja EE-ASA:lla, noin 65 Nm/g
Kuusi stabilointiainetta valittiin likaantumiskokeisiin, joissa käytettiin ASA-emulsioiden ja saostetun kalsiumkarbonaatin CaCO
3
(PCC)

seoksia. Stabiileimman emulsion, parhaan liimauksen ja vähiten likaavan emulsion tuottivat referenssitärkkelys kummallakin ASA:lla,
6.C-PAM EE-ASA:lla ja PAAE puhtaan ASA:n kanssa. Keskimäärin kumpikaan ASA ei tuottanut toistaan huomattavasti vähemmän
likaavia emulsioita, vaan kummallakin saavutettiin sekä hyviä että huonoja arvoja. Pintojen lian luonteessa oli huomattavia eroja. PAAE
emulsioiden lika lähti helposti näytemetallilevyjen pinnoilta. Sen sijaan referenssitärkkelys emulsioiden lian irrottaminen olisi vaatinut
kemiallisen käsittelyn liatuille metallipinnoille.
Kustannussäästöjä voidaan saavuttaa 6.C-PAM:lla, ja PAAE:llä. Tärkkelyksellä ei ollut juurikaan eroa kahden ASA:n välillä, 6.C-
PAM:lla EE-ASA toimi paremmin ja PAAE:llä puhdas ASA tuotti optimaalisia tuloksia. PAAE:n positiiviset vaikutukset paperin märkä-
lujuusominaisuuksiin tekevät kemikaalista kaupallisessa mielessä kiinnostavan.
Työn valvoja Työn ohjaaja
Prof. Janne Laine FT Juha Lindfors
Professuuri Koodi
Puunjalostuksen kemia Puu-19
Sivumäärä Kieli
100 + 8 Englanti
Avainsanat Päiväys
emulsio, emulgointi, ASA, massaliimaus, paperi 13.11.2009


ACKNOWLEDGEMENTS
This master’s thesis was made together with Kemira Ltd and Helsinki University of Tech-
nology (TKK) and was financed by Kemira Ltd. The thesis was written in between April 14,
2009 - November 13, 2009.
Professor Janne Laine from TKK supervised the thesis and the instructor was research scien-
tist Juha Lindfors, D.Sc. (Tech.) from Kemira Espoo Research and Development Center,
Wet-End Chemistry. I want to thank them for their support and guidance during the process.
My gratitude goes also for the manager of the Espoo Wet-End Chemistry sizing team, Reetta
Strengell, M.Sc., for research scientist Anneli Lepo, M.Sc. at Espoo Wet-End Chemistry and
to research scientist Taina Leino, M.Sc. at TKK. They helped me put together a good deal of
my theoretical studies and had many guiding opinions for experiments during the process.
Laboratory technician Katja Halttunen is thanked for paper testing and giving helpful hints

during the experimental work.
Thanks is also extended to Kyle Kettering, B.A., who read the manuscript and helped with
the grammar of this thesis
The enormous efforts of my parents to always encourage me are also worth of special men-
tion and sincere gratitude. My father, Jarmo Merisalo – an experienced papermaker himself
has kept me constantly looking forward. It is a privilege to represent the third generation of
papermakers in the family.

Finally, I want to thank my wife, Heidi, for her unconditional love and care during the thesis
writing process. You and the baby you are carrying have been a constant source of inspira-
tion. Proverbs 31:28-29.

In Espoo, November 24, 2009


Jarno-Petteri Merisalo


TABLE OF CONTENTS
1 INTRODUCTION 8
LITERATURE PART
2 EMULSIONS 9
2.1 Properties 9
2.2 Interfaces and surface interactions 11
2.3 Surfactants 15
2.4 Stabilization 19
2.5 Destabilization 22
2.6 Emulsification process 26
2.7 Emulsification equipment 28
2.7.1 Rotor-stator homogenizator 28

2.7.2 Colloid mill 28
2.7.3 Ultrasonic homogenizer 29
2.7.4 High shear machinery 29
2.7.5 Produced particle sizes 30
2.8 Examples of different emulsions 31
2.8.1 Food industry 31
2.8.2 Medical industry 32
2.8.3 Cosmetic industry 32
2.8.4 Agricultural emulsions 33
2.8.5. Inks 33
2.8.6. Asphaltic bitumen 34
2.8.7 Nano- and microemulsions 34
2.8.8 Paper and board industry 35
3 INTERNAL SIZING OF PAPER AND BOARD 38
3.1 The purpose of sizing 38
3.2 Sizing chemicals 40
3.2.1 Reactive sizing agents 41
3.2.2 Rosin sizing agents 41
3.3 Effect of fillers on internal sizing 42
3.4 Effect of retention on internal sizing 43
4 ALKENYL SUCCINIC ANHYDRIDE SIZING 45
4.1 Chemistry and reactions 45
4.2 ASA in paper- and boardmaking process 49
4.3.1 Emulsification 51
4.3.2 Stabilization 53
4.3.3 Additives in ASA sizing 54
4.3 ASA internal sizing compared to other sizing systems 55
EXPERIMENTAL PART
5 OBJECTIVES AND EXPERIMENTAL PLAN 59
6 MATERIALS AND METHODS 61

6.1 Materials 61
6.1.1 ASA sizing agents 61
6.1.2 Emulsion stabilizers 61
6.1.3 Pulp 66
6.1.4 Other chemicals 66
6.2 Methods and equipment 66
6.2.1 Emulsion preparation 66


6.2.2 Emulsion measurements 67
6.2.3 Paper hand sheet preparation 69
6.2.4 Paper hand sheet testing 70
6.2.5 Deposition testing 70
7 RESULTS AND DISCUSSION 73
7.1 Emulsion stability 73
7.2 Properties of the hand sheets 79
7.3 Deposition tendency of the emulsions 82
8 CONCLUSIONS 86
REFERENCES
APPENDICES



LIST OF ABBREVIATIONS
A-PAM Anionic polyacrylamide
A-VAM Polyamide derivative
AB Acid-base
AKD Alkyl ketene dimer
ASA Alkenyl succinic anhydride
C-PAM Cationic polyacrylamide

CaCO
3
Calcium carbonate
CaO Calcium oxide
CaSO
4
Calcium sulphate
CMC Carboxymethyl cellulose
cmc Critical micelle concentration
CO
2
Carbon dioxide
-COOH Carboxyl group
DELSA Doppler electrophoretic light scattering analyzer
DS Degree of substitution
EE-ASA Easy emulsifying alkenyl succinic anhydride
G-PAM Glyoxylated polyacrylamide
GCC Ground calcium carbonate
GGM Galactoglucomannan
HCD High charge density
HLB Hydrophile-lipophile balance
HMW High molecular weight
LCD Low charge density
LMW Low molecular weight
LW Lifshitz-van der Waals
MCD Medium charge density
MMW Medium molecular weight
NaOH Sodium hydroxide
-OH Hydroxyl group
P-VAM Polyvinyl amine

PAC Polyaluminun chloride
PAAE Polyamidoamine-epichlorohydrin
P-DADMAC Poly diallyl dimethyl ammonium chloride
PCC Precipitated calcium carbonate
PIT Phase inversion temperature
PVA Polyvinyl alcohol
SR Schopper-Riegler
TGA Thermal gravimetric analysis
TiO
2
Titanium dioxide
TNT Trinitrotoluene
vdW van der Waals

8
1 INTRODUCTION
Emulsions are used in all fields of chemical industry, food, pharmacy, cosmetics, agri-
cultural and paper- and boardmaking among others. The emulsion properties and emul-
sion preparation are affected by the choice of continuous and discontinuous phases of
emulsion, stabilizing substances, and surface active agents. In typical emulsions, the
discontinuous phase drops are covered with stabilizing agents, called stabilizers. Stabi-
lizers are nonionic or ionic polymers and microparticles. Emulsions can be optimized
for specified use by selection of stabilizers. Molecular weights, degrees of substitutions
and charge densities of stabilizers can affect the generated emulsion.
By modification of emulsion particle size, affected by shear force, shear time and
preparation amount, the emulsification event can be optimized. Other control variables
in emulsion preparation are, for example, concentration, pH and temperature. In paper-
making, notable cost savings can be gained by a correct sizing agent and right sizing
properties /1, 2/. It is defined as addition of the sizing agent to the stock in the wet-end
of the paper machine before the wire section, to make paper more hydrophobic /3, 4/.

In literature part, for example, stabilizers, surface active agents, emulsions and emulsi-
fication techniques are discussed. The related theories are studied in order to adopt the
information from other emulsion fields into the field of paper and board internal sizing
emulsions. The impact of different surface active substances on sizing emulsion proper-
ties and functionality are presented. The internal sizing emulsions of Alkenyl Succinic
Anhydride (ASA) are more widely examined in order to optimize the adjustability and
cost-efficiency of commercial ASA in paper and board internal sizing. Comparison
with other internal sizing agents, such as Alkyl Ketene Dimer (AKD) and rosin sizing
agents are presented to understand better the pros and cons of the internal sizing agents.
In experimental study, two types of ASA's were used in emulsification experiments
with over thirty stabilizers, including ionic and nonionic stabilizers and microparticle
systems. The effects of stabilizer molecular weight or degree of substitution, charge
density, presence of surfactants and emulsion particle size to the end product properties
were all studied. Selected ASA-stabilizer emulsions were used for paper hand sheet
preparation and hydrophobation, and to deposition tests with a specific device used by
Lindfors /5/. The goal was to use experimental results in proposing ASA internal sizing
systems for customers which’s other process conditions are known.

9
LITERATURE PART
2 EMULSIONS
The International Union of Pure and Applied Chemistry (IUPAC) defines emulsion the
following way: "An emulsion is a dispersion of droplets of one liquid in another one
with which it is incompletely miscible. Emulsions of droplets of an organic liquid (an
oil) in an aqueous solution are indicated by the symbol O/W and emulsions of aqueous
droplets in an organic liquid as W/O. In emulsions the droplets often exceed the usual
limits for colloids size." /6/.
Another definition by Becher is: "An emulsion is a heterogeneous system, consisting of
at least one immiscible liquid fully dispersed in another in the form of droplets, whose
diameters, in general, exceed 0.1 µm. Such systems possess a minimal stability, which

may be amplified by additives for example surface active agents and finely-divided sol-
ids." /7/.
Microemulsions are defined as a thermodynamically stable emulsion, while macroe-
mulsions are not thermodynamically stable /6/. The thing that makes a liquid-liquid dis-
persion an emulsion is the fact that one immiscible liquid is dispersed in another, stabi-
lized by a third component, called emulsifying agent /8, 9/.
Emulsions can be divided in two categories, two-phase emulsions and three or more-
phase emulsions, of which W/O, O/W, W/O/W and O/W/O are examples /10/. Further
on, emulsions can be divided based on discontinuous phase particle size, nano or mini-
(10-100 nm), micro- (100-1000 nm), and macro- (0.5-100 µm) emulsions. Other divi-
sions are based on the emulsion preparation process, low shear, high shear, high energy
and ultrasound emulsification, or on field of use, for example, cosmetic, medical, agri-
cultural, petroleum, food or papermaking emulsions /11/.
2.1 Properties
Important emulsion properties are emulsion particle size, stability, charge, pH and tem-
perature. Charge and temperature dependence are typical characteristics in macroemul-
sion. Stability is affected by controlling temperature, pH and by selection of component
charges. The particle size is the most important single property of an emulsion. Particle
sizes are expressed as particle size distribution that can be labeled as monodisperse,
polydisperse, symmetrical or asymmetrical, unimodal or polymodal. With microemul-
sions the situation is somewhat different due to the very small particle size and the same

10
division does not apply. While particle size is related to drop surface area, it has a major
effect on reactivity and stability. In general, the smaller the drop, the higher viscosity
exists in the emulsion. Particle size, or droplet diameter, of an emulsion is usually not
completely uniform. This is why particle size distributions are used. The particle size of
an emulsion is affected by the amount and time of shear during emulsification and by
the choice of stabilizer. From Figure 1, typical emulsion particle sizes and appearance
can be seen. /7, 12/

Figure 1. At the top, the dimensions of dispersed phase for liquid-liquid dispersions in µm, and at the
bottom, the typical dispersion appearance in emulsions, can be seen. In the center are schematic
drawings of stabilized emulsion oil drops in water /13/.
The particle size distribution is a result of emulsification and thus has important infor-
mation about the emulsion properties. If 10 m
3
of oil is emulsified to the drop radius of
1 µm (1x10
-6
m), the total interfacial of area created is 3x10
7
m
2
, while the unemulsified
oil surface area is 22.4 m². The increase of surface area is over million fold, adding the
significance of the surface and interfacial properties /7/.
The particle size characterizes many properties of emulsion: viscosity, solubility, reac-
tivity, and emulsification all depend on particle size. This is because emulsions are pre-
pared by breaking drops and coalescence, i.e. the disappearance of the boundary be-
tween two particles, which can be droplets or bubbles in contact. This can also occur
with the disappearance of boundary between a particle and a bulk phase followed by
changes of shape. Coalescence leads to a reduction of the total surface area. The floccu-
lation of an emulsion, the formation of aggregates, may be followed by coalescence
/14/.

11
2.2 Interfaces and surface interactions
When two immiscible liquids are placed in contact, an interface is formed /15/. Since
changes in emulsion appearance and properties occur in emulsion phase interfaces, the

surfaces, forces, and charges between them are discussed. Surface tension is defined by
the equation 1. A force F moving liquid surrounded by a plate CD at the length of Δd
from point CD to C´D´, requires a work w done on the liquid for the movement. The
force F is balanced by a counter-force operating along the length CD. If γ is defined as
the force in Newtons per meter acting along this length, Δd, the force opposing the ex-
pansion of the film is 2γl. The surface tension γ can be defined as the work needed to
generate a surface (Figure 2).
S
w
SdldFw
Δ
=⇔Δ=Δ=Δ=
γγγ
2
(1)

l
A
BC
DD´
C´
Δd
F
l
A
BC
DD´
C´
Δd
F

Figure 2. The physical definition of surface tension /7, 16/.
While surface tension only relates to surfaces between a liquid and a gas, the concept of
interfacial tension describes also the boundary tensions existing between two liquids
and between a liquid and a solid phase. Adhesion between two substances or particles is
defined as the work that needs to be done to separate two surfaces from one another.
The force resisting the separation work between two different material surfaces is called
adhesion. Work of adhesion and free energy of adhesion are defined in equation 2. Il-
lustration of adhesive forces is given in Figure 3. /17, 18/
Where,
w is the work done for moving the plate [Nm].
F is the force required for the moving work [N].
Δd is the distance the plate moves [m].
γ is the surface tension [N/m].
l is the length of flank AB, CD and CD´ [m].
ΔS is the surface area the plate movement outlines [m
2
].

12
21
*
1221
ππ
γγπ
γ
γ
γ
+==
−=

−
+
=
AA
lvlL
A
WW
W
(2)

A
B
A
B
A
B
A
B

Figure 3. When cylinders A and B of pure liquids are pulled apart from their mutual interface, work
equal to the work of adhesion W
A
is required.
When a drop of liquid is dropped onto a smooth surface, adhesive forces affect between
the solid and the liquid phase. If these forces are greater than the internal adhesion
keeping the liquid together, the drop will spontaneously spread and perfectly wet the
surface. In a balance between the adhesion of liquid and solid and the liquids internal
adhesion, the drop forms a contact angle at the phase interface (Figure 5) /4, 5, 17, 19/.
In solid-liquid interfaces the liquid can spread in three different ways on top of a sur-
face. These are: forming a contact angle with the surface, spreading completely on the

surface, or adsorbing onto the surface and then forming a contact angle (Figure 5). Ad-
sorption is an accumulation of a substance onto a surface /3, 15/. A contact angle is
formed if the spreading of a liquid on a solid is not complete. The more hydrophobic
(i.e. water resistant) the surface is, the bigger contact angle water drop forms with the
surface.
Where,
W
A
is the work of adhesion [J/m
2
].
γ1 is the interfacial tension of surface 1 [J/m
2
].
γ2 is the interfacial tension of surface 2 [J/m
2
].
γ12 is the interfacial tension shared between surfaces 1 and 2 [J/m
2
].
πL is the liquid pressure [Pa].
γl is the interfacial tension in the liquid [J/m
2
].
γlv is the interfacial tension in liquid-vapor interface [J/m
2
].
WA* is the work of adhesion with vapor pressure [Pa].
π1 is the partial pressure of surface 1 [Pa].
π2 is the partial pressure of surface 2 [Pa].

13

Figure 4. The three spreading ways of a liquid on a solid surface: A; the liquid does not wet the solid
surface but forms a finite contact angle on the surface, B; the liquid wets the solid surface completely
forming a separate layer with the surface, C; some of the liquid molecules adsorb onto the solid sur-
face but others form a contact angle./20/.
In a case that a finite contact angle is formed, the equilibrium balance between the in-
terfacial tension of the solid surface, liquid drop, and the vapor phase is expressed with
Young's equation (equation 3) /21/.
lv
slsv
γ
γ
γ
θ
−
=cos
(3)

Between the different particle systems and interfaces in emulsions, attractive and repul-
sive forces are seen. These forces are electrostatic, or van der Waals (vdW) forces. The
vdW forces are interactions between absorbed molecules and hydrodynamic forces /15/.
The net attractive forces operating on a molecule in the interface are a combined effect
of vdW interactions and the individual surface tensions of the two liquids. This is ex-
pressed in the theory of diffuse layer, which states that the layer forms from free ions in
the fluid under the influence of electric attraction and thermal motion. In emulsions,
intermolecular interactions can be divided into three groups, short-range repulsion be-
tween electron orbitals (Dorn repulsion), Lifshitz-van der Waals (LW) interactions, and
Lewis acid-base (AB) interactions.

Dorn repulsion indicates itself in the incompressibility of liquids and solids. LW forces
occur between all atoms and molecules and are due to the permanent and transient di-
pole moments created by the distribution and movements of electrons in the molecules.
They are attractive and decrease with distance. AB forces interact between electron do-
nor groups in one molecule and electron accepting groups in another. The influence of
Where,
θ is the definite contact angle between liquid and solid phase [°].
γ
sv
is the interfacial tension between solid-vapor interface [N/m].
γ
sl
is the interfacial tension between solid-liquid interface [N/m].
γ
lv
is the interfacial tension between liquid-vapor interface [N/m].

γ
sl
γ
sv
γ
lv

14
different functional groups on the adhesive properties of surfaces can be explained with
AB interactions. /16/
Two surfaces in contact attract each other due to the LW forces. Because work is re-
quired to separate the surfaces, the aggregated state is thermodynamically more stable
than the dispersed state. If the surfaces are separated in a liquid, the situation is differ-

ent. If the liquid wets the surface completely, the particles can emulsify spontaneously.
However, the fluid between the surfaces tends to reduce the attraction of the surfaces,
being unable to generate colloidal stability. Stable colloids (i.e. 0.01-1 µm size mate-
rial) can be prepared in many liquids which do not reduce attraction to zero. The repul-
sive and attractive interactions are additive properties. Depending on the range and
strength of the interactions, different situations occur.
The vdW interactions are very strong at short distances and quite significant at dis-
tances of relevance to colloidal stability. An important property of the vdW forces is
their universality. If the particles are set in a medium, the interactions distance depend-
ence does not change, but the magnitude of the forces are reduced due to the vdW inter-
action between the liquid and the particles. vdW forces can be divided into three spe-
cific types: Keesom forces, acting between two dipoles, Debye forces, acting between a
dipole and an induced dipole, and London forces, acting between two induced dipoles.
/15/
The Derjaguin-Landau-Verwey-Overbeek (DLVO) theory of colloidal stability assumes
that the van der Waals forces between surfaces are independent of electrolyte concen-
tration and particle charge, and that the electrostatic interactions are solely due to dif-
fuse double layer interactions in a solution /16/. Due to the charge neutrality in an elec-
trostatic double layer system, the charge balance develops between the charges on the
surface and the free ions in the solution. Equilibrium is developed between the attrac-
tion of the counter ions to the surface and the diffusion away from the surface. The re-
sult is a potential difference between the particle surface and the neighboring liquid
/15/. The potential differences at the given distances from the particle surface are called
layers (round the particle).
When fine particles are dispersed in water, an electric charge is developed on the parti-
cle surface. The origin of this charge can be one of the three following; ionizable
groups on the particle surface (for example -COOH), isomorphous substitution in the
crystal lattice (faults and lattice disturbances), or adsorption of ions at the interface. The
electrostatic attraction is a consequence of the surface charges whereas the vdW forces

15
depend on the chemical nature of the solid phase. The counter ions at the charged sur-
face are affected by three forces: electrostatic attraction, vdW forces and thermal
movement. The interactions that influence colloidal stability are long-range compared
to the interactions that govern the adhesion between surfaces in molecular contact.
Typical distances range from 1 nm to 100 nm /15/.
In emulsions, their viscous properties change during time. In aggregated emulsions, the
aggregate size increases over time because of the thermodynamical instability. These
aggregates immobilize liquid from the continuous phase within the voids between the
drops. Macroemulsions are practically never monodispersed, so that one phase would
be perfectly mixed into another /13, 22/. Non-uniform drop size (i.e. particle size distri-
bution) influences rheological properties. Hydration of the stabilizer and/or surface-
active substance layer adsorbed around the oil drops in an emulsion will also influence
the rheological properties. If the stabilizer is hydrated on the emulsion oil drop, the sta-
bilizing effect can be lost. The high electric field strength at the particle surface leads to
adsorption of water molecules and to an apparent increase in drop radius. The addition
of electrolyte alters the degree of hydration. Then the effective thickness of the hy-
drated adsorbed stabilizer layer decreases, as the electrolyte concentration increases.
/22/
2.3 Surfactants
Surfactants are surface active substances with various tasks in surface chemistry. In lit-
erature, the word emulsifier is commonly used in referring to any substance giving sta-
bility on emulsion discontinuous phase droplets or making the emulsification easier by
lowering surface energies /6, 8, 9/. The problem arises when more than one chemical is
used for the purpose at the same time. To avoid confusion in this study, the word sur-
factant is used when referred to surface active agents and word stabilizer is used when
referred to those stabilizing agents used on the emulsion oil drop alone. Another catego-
rization in literature is presented by Chen /2/.

16

Figure 5. Schematic picture of a surfactant with hydrophilic head group and hydrophobic tail groups
/23/.
Surfactants have dualistic amphiphilic character, which means one end is hydrophilic
and the other hydrophobic (Figure 5). Surfactants adsorb at the interface between two
phases of emulsion due to their amphiphilic molecular structure. They reduce the sur-
face free energy required to increase any interfacial area by lowering the interfacial ten-
sion and allowing the finely dispersed media to easily be created /24, 25/.The phase
diagram of a surfactant in emulsion is presented in Figure 6.

Figure 6. Schematic phase diagram of surfactant, oil and water systems. Outside the composition
triangle, surfactant nano and microstructures in various phases are indicated /23/.
The surfactant degree of hydrophilicity or hydrophobicity is expressed by the hydro-
phile-lipophile balance (HBL), lipophile meaning hydrophobic. Emulsion surfactants
can be characterized by their HBL value. The scale goes from 0 to 20. In general, val-
ues above 7 refer to hydrophilic surfactants and those below 7 to hydrophobic ones. The
difference of surfactants is generally expressed by the HLB number, with the more oil

17
soluble surfactants having low value and the more water soluble ones having high value
of HLB /26/. This index is used to describe emulsion stability with many types of sur-
factants in all kinds of emulsions. /13, 27, 28/
For nonionic surfactants in general, a ratio between the hydrophilic saponification
number and hydrophobic (lipophilic) acid number is in use to determine the HLB num-
ber. Specific equations exist, for example for, fatty acids and surfactant mixtures based
on emulsion droplet coalescence. A logarithmic HLB scale for mole fractions of surfac-
tants with many other group-specific methods, have been developed because the HLB
number is an empirically defined quantity. A summarizing table of the HLB number
effect on different surfactants is presented (Table 1). /7, 13, 15, 17/
Table 1. HLB number ranges and their application /7/

HLB number range Application
3-6 W/O Emulsifier
7-9 Wetting Agent
8-18 O/W Emulsifier
13-15 Detergent
15-18 Solubilizer


– The size of emulsion droplets depend on the temperature and the HLB
number of surfactants.
– The droplets are less stable toward destabilization close to the PIT.
– Relatively stable O/W emulsions are obtained when the PIT of the system
is some 20 °C to 65°C higher than the storage temperature.
– A stable emulsion is obtained by rapid cooling after formation at the PIT.
– Optimum stability of an emulsion is relatively insensitive to changes of
HLB value or PIT of the surfactant.
– Instability is very sensitive close to the PIT of the system.

Phase inversion temperature (PIT) is the temperature where a nonionic or ionic surfac-
tant changes its appearance (Figure 7). The PIT of surfactants is influenced by the cor-
responding HLB value. The phase difference in emulsions exists mainly because of the
difference in isotropic characteristics between the phases. The following conclusions
can be made about the PIT /29/:

18

Figure 7. Phase diagram of CH
3
(CH
2

)11O(CH
2
CH
2
O)5H (orC
12
E
5
), n-octane and water. Schematic
drawings of different surfactant aggregates shape development in various points and phase transi-
tion can be seen /23/.
At the temperatures near the PIT, high solubilization of surfactant particles occur and
the emulsion particle size may become very small if much surfactant is present, even
with just a gentle stirring. The dependence of HLB and PIT leads to the conclusion that
the addition of salts reduces the PIT and thus a surfactant with a high PIT value is
needed in the presence of electrolytes (i.e. substance containing free ions) in order to
obtain a more stable emulsion /29, 30/. An example on the presence of electrolytes can
be taken from papermaking. ASA compound and Ca
2+
ions can both be seen in paper
and board machine water system. Hydrolyzed state ASA compound has lost its stability
brought by a stabilizer and/or surfactant on its surface. In this state, ASA easily forms
ASA-Ca
2+
salt, affecting the process cleanliness and runnability. ASA-Ca
2+
complexes
are seen in deposit tests with various emulsions.
Surfactant head group surface area divided with the surfactant tail group surface area
has significant effect on the stabilization efficiency of a surfactant /31/. This ratio de-

fines the surfactant hydrophilicity or hydrophobicity. The relative size or the surface
area of the head group (Figure 5) and the surface area of the tail group turns the overall
nature of the surfactant roughly to either hydrophilic or lipophilic and the outcome can
be determined by HBL number.
Surfactants in emulsions can form spontaneously larger ordered structures. This results
because in an aqueous surfactant solution, the properties change quickly around a rela-
tively small concentration range. Stable aggregates are formed if large enough mono-

19
mers come together forming a micelle of 15-100 surfactant monomers /16/. Micelles
form above a certain concentration limit called the critical micelle concentration (cmc)
(Figures 6 and 7). While the thermodynamic properties such as surface tension and con-
tinuous phase activity change slowly above this concentration, a rapid increase in tur-
bidity, (i.e. the light scattering properties of an emulsion), is seen. Turbidity increases
with decreasing emulsion particle size /2/.
Above cmc large aggregates of micelles are formed and the aggregation process is co-
operative. Most of the surfactant added in excess of cmc is incorporated into the mi-
celles. The monomer concentration increases very slowly, and the chemical potential of
the surfactant is almost constant above the cmc. When the concentration of cations in-
creases, micelle formation is promoted and any addition of electrolyte also lowers the
cmc. /16/
When an emulsion of a nonionic surfactant, or stabilizer, and hydrocarbon in water is
heated, the emulsion becomes visibly turbid at a temperature known as the cloud point.
At this temperature or slightly higher, the emulsion separates into a surfactant and/or
stabilizer rich phase and to a water rich phase. Conversely, if the emulsion is cooled, a
temperature called the haze point exists. Below the haze point, an oil-rich phase and a
surfactant rich phase form. In the case of O/W emulsions, shorter surfactant chains en-
hance solubilizing power for a given length of surfactant hydrocarbon chain. In the case
of W/O emulsions, inverse micellar phenomenon is seen (Figures 6 and 7). If the tem-
perature of O/W emulsions is increased after reaching the cloud point, the surfactant

phase coalesces with the hydrocarbon phase to form a W/O emulsion and the PIT is
reached. /32/
2.4 Stabilization
Macroemulsions are thermodynamically unstable systems and thus aggregation occurs.
For this reason, emulsion oil droplets must be stabilized using stabilizers and/or surfac-
tants. Reasons for stability are related to emulsion droplet collision frequency and to
emulsion energy barrier. In collision frequency, the colloidal particles (i.e. stabilizer
and emulsion oil drops) can collide so rarely that the rate of aggregation becomes neg-
ligible. This cause is valid only in very dilute emulsions. The second case is relevant if
there is an energy barrier which prevents particles from transferring to the thermody-
namically more stable (aggregated) state. Then aggregation will not occur. Energy bar-
rier can cause stability if repulsive interactions in emulsion are weaker than attraction at

20
short distances, but stronger than attraction at intermediate distances /15, 16/. Accord-
ing to Abismail, emulsion stability depends on /24/:

1. Emulsion droplet size.
2. Density difference between emulsion dispersed and continuous phases.
3. Viscosity of the emulsion continuous phase.
4. Electrostatic and or steric repulsion between emulsion droplets.
Stabilizers and surfactants have significant effect on these repulsions.

In macroemulsions, emulsion droplets can be stabilized against coalescence by poly-
mers, surfactants or by nano- and microparticles. Stabilizers are non-surface active
macromolecules added to increase the viscosity of the continuous phase and to reduce
the mobility of droplets in order to prevent them from breaking up the emulsion – a
phenomenon called demulsification /7/. After a viscosity increase, the droplets become
cylinder-like and eventually lamellar (Figure 7). Stabilizers make emulsion stable steri-
cally, electrostatically or by small particle stabilization which is one type of steric stabi-

lization. Surfactants can be used solely or with stabilizers. The effect of surfactants is
usually dualistic, they can have the stabilizing effect on the emulsion oil droplets, but at
the same time, they ease the emulsification process itself /25/. Copolymers are another
option to use with the actual stabilizer. Copolymers as well as other stabilizers and sur-
factants are not always but often synthetic. /16/
Steric stabilization, also called protective colloidal effect, is the general term for the
stabilization of colloidal particles with non-ionic, soluble, polymers. If a particle or
droplet surface is covered with a polymer which extends into the emulsion continuous
phase, the polymer segments prevent the adhesion of the particle to other particles. The
polymeric layer functions as a steric barrier against aggregation. When charged stabi-
lizers are used for stabilization, the electrosteric stabilization is in question.
Polymers used as steric stabilizers should adsorb so strongly to the emulsion discon-
tinuous phase surfaces that they do not desorb even when subjected to the shear forces
occurring when particles collide (Figure 8). Other extensively used steric stabilizers
than polymers are hydrophobically modified polysaccharides /33/. With this stabiliza-
tion mechanism, the solubility of the adsorbed polymer chains is significant for the sta-
bility of the emulsion. The stabilization changes the behavior of the contact surface.
/16/

21

Figure 8. At left, oil-in-water emulsion (O/W), surfactant tails form the core of an aggregate; at right
water-in-oil emulsions (W/O) the heads of the surfactants are in the core /34/.
A Pickering emulsion is an emulsion stabilized by nano or micro scale solid particles
which adsorb onto the interface between the water and oil phases (Figure 9) /35/. When
oil and water are mixed, small oil droplets are formed and dispersed throughout the wa-
ter. Eventually the droplets will coalesce to decrease the amount of energy in the sys-
tem. However, if solid particles are added to the mixture, they will bind to the surface
of the interface and prevent the droplets from coalescing, causing the emulsion to be
more stable. Hydrophobicity, shape, and the size of the particles can all have an effect

on the stability of the Pickering emulsion. It is thought that the presence of solid parti-
cles at the liquid/liquid interface plays an important role in preventing the thinning of
the liquid film between the droplets. Solid particles should form a continuous one-
particle-thick film onto emulsion discontinuous phase droplet. This is why rough,
asymmetric particles like bentonite are more efficient than smooth spherical silica parti-
cles in this task. /29, 36, 37/

Figure 9. If nano- and microparticles with diameters ranging from 8 nm to 500 nm are used, instead
of adsorption the particles adhere in the phase interface. At left, oil-in-water (O/W) emulsions, at
right water-in-oil (W/O) emulsion /34/.
Surfactants may stabilize the emulsion discontinuous phase droplets in four ways /16,
25/. In the first case, the surfactant may be nearly insoluble and remain crystalline
without swelling much with water. This is usually at a temperature well below the melt-

22
ing point of the surfactant. In the second case, the surfactant may dissolve readily in
water. Dissolution is accompanied by surfactant spontaneous forming of micelles.
The third case is that the hydrophobic chains are oriented inward and the polar end
groups form a hydrophilic shell (Figure 8). Surfactant micelles have the capacity to dis-
solve water-insoluble compounds inside of them. At concentration exceeding solubility,
lyotropic liquid crystals, called mesophases are formed. These consist of rod-like or
lamellar surfactant aggregates that are organized into defined structures (Figure 6). Al-
though the aggregates show long-range ordering, they are flexible, and the surfactants
are still mobile within the aggregates.
The fourth case is with very hydrophobic surfactants, which do not dissolve in water at
all. However, when contacted with water at temperatures above their melting point,
they may form aggregates in which an aqueous core is surrounded by a surfactant layer.
These aggregates are called inverted, or reverse micelles (Figures 6 and 7). They also
form a reverse hexagonal liquid crystalline phase in which the micelles have grown to
infinite rods arranged in a hexagonal shape forming a lattice (Figure 6).

The stability is a balance of attractive and repulsive interactions at interfaces. The same
interactions stabilize thin liquid films in foams between emulsion droplets and on sol-
ids. They are affected by adsorption of stabilizers and/or surfactants, ionic strength, dis-
solution and temperature. The stability of macroemulsions is independent of the nature,
size, and shape of the particles in emulsion and dependent only on the interaction of the
stabilizer with continuous phase temperature. /15/
Stabilizers and/or surfactants on emulsion discontinuous phase droplets can be differ-
ently saturated. This means that the surface coverage of the droplet by the stabilizer can
be incomplete, complete, or over-filled. The surface coverage has an influence on the
operations of the stabilizer and the behavior of the flock formed. The charge of the sta-
bilizer polyelectrolyte also has an effect, whether it is high, medium or low charged,
cationic or anionic.
2.5 Destabilization
Aggregation, in which terms flocculation and coagulation are also used, takes place in
emulsions. Particles of discontinuous phase form larger complexes called aggregates
/38/. Depending on the formulation process of an aggregate, it is given the more spe-
cific name of floc or coagulant. Coagulation is an aggregation phenomenon occurring
due to the loss of stability in emulsion. The complete distinction between flocculation

23
and coagulation is impossible because of many causative mechanisms, thus the general
term aggregation is used. Regarding the distinction between aggregation and coales-
cence, one can roughly say that coalesced emulsion can be returned in the mixed emul-
sion state by applying shear (manual shaking), in it but to aggregated emulsions this
makes no difference. Aggregation mechanisms are charge neutralization, electrical
double-layer compression, patch model, bridging and complex flocculation /39/.
Figure 10 shows the destabilization events in emulsion /29/. Flocculation and creaming,
for example, can occur simultaneously /40/.The deformation and flow of an emulsion
depends on continuous and discontinuous phase rheological properties, meaning the
viscosity of water and oil phase. The reason oil phase is used in the form of an emulsion

rather than in its original state is the much wider range of flow characteristics and con-
sistencies that can be achieved in an emulsion.

Figure 10. The destabilization phenomena in an emulsion. In the center up, stable O/W macroemul-
sion which flocculates due to the thermal instability during time causing one or many of the five
changes in emulsion /24/.
According to DLVO theory, vdW attraction forces are the driving forces for coales-
cence and destabilization of an emulsion. For sterically stabilized emulsions the vdW
interactions can be neglected if the whole oil droplet surface is completely saturated
(i.e. covered with stabilizer), and if the molecular weight of the separate stabilizing
chain segments is high /15/. Table 2 summarizes the effect of different parameters on
colloidal interactions in emulsions according to the DLVO theory.


24
Table 2. Factors affecting colloidal stability in emulsion according to DLVO theory /16/
Parameter
T
he effect of parameter value increase on colloidal stabilit
y
Surface charge density increase Increases
Electrolyte concentration increase Decreases
Counter-ion valence difference Decreases
Hamaker constant increase (vdW particle interactions) Decreases
Temperature increase Decreases or Increases
Dielectric constant of the solvent increase Increases

Sedimentation and creaming is seen in phases with density differences. Aggregation
occurs when droplets stay very close to one another for a far longer time than they
would in the case with no attractive forces acting between them. Coalescence is seen

when a thin film of continuous phase between two closely approaching droplets break.
Laplace pressure, the pressure difference between inside and outside of the emulsion oil
droplets, then causes the droplets to rapidly fuse into one droplet. If the droplets contain
solid particles because part of the liquid in the droplets has frozen, full coalescence may
not occur. In this case the terms clumping or partial coalescence are used. /27/
Particles forming an emulsion undergo irregular thermal back and forth movement
called Brownian motion. It is caused by the molecules of the discontinuous phase that
are bombing the emulsion particles. This phenomenon is seen with small particles in
emulsion. Brownian motion increases the inter-particle collision probability, i.e. coagu-
lation risk and destabilization of nano- and microemulsions and also small droplet sized
macroemulsions. /7/
Five interactions play important roles in instability over time, leading to emulsion de-
stabilization – a phenomenon called coarsening process /41/. These interactions are:

1. vdW forces between neighboring particles or droplets. Such interactions
cause film instability during the late film drainage state.
2. Random mechanical forces exerted on dispersed particles by Brownian
motion.
3. Capillary forces causing the further relaxation of a dumbbell-like
particle to a sphere.
4. Buoyancy, resulting from the different gravities of two components that
can be neglected for systems with little difference in density. Buoyancy
makes the particles move directionally and causes the formation of a
gradient of particle size distribution.
5. Friction resulting from viscous flow that is induced by the vdW,
Brownian, capillary, and buoyancy forces.


25
When the repulsive energy is low, particle collisions will lead to aggregation, or more

specifically coagulation. If there is no repulsive barrier (i.e. stabilizer) at all, coagula-
tion can take place within seconds. In most cases the barrier is not high-energetic
enough to completely prevent the aggregation. These types of emulsions coagulate
slowly. The change in repulsive energy depends on the temperature, nature of the ad-
sorbent on the surface, ionic strength, solvent, and stabilizer particle charge. These offer
the possibility to control aggregation and stability by appropriate choice of parameters.
When coagulated gas bubbles (liquid droplets or foams in the emulsion) join together to
coalesce forming larger bubbles or droplets, the total surface area of particles decreases.
The surface energy of the system decreases, establishing an important driving force for
the removal of particles. An indication of the driving force of the particle removal is
called Ostwald ripening (Figure 10). Few emulsion droplets grow in size, at the cost of
majority shrinking and disappearing /42/. It involves diffusion of discontinuous phase
material from smaller to larger droplets due to the chemical potential of the material
being higher for a smaller radius of curvature. Ostwald ripening does not occur if the
solubility of the continuous phase droplets is insignificant. /16, 27/
A sterically stabilized emulsion cannot be destabilized by adding electrolyte, unless the
stabilizer is desorbed from the emulsion oil droplet surface at the same time. Aggrega-
tion can be done by reducing the solubility of the polymer in the continuous phase. In
this case, a collapse of the polymer conformation is achieved and the stabilizing effect
is lost. The simplest way to aggregate macroemulsion droplets is to change the tempera-
ture of the solvent. When the solubility is reduced, there is a sharp transition from long-
term stability to instability in the emulsion. Depending on the types of interaction which
exist between the liquid state and the adsorbed stabilizer, instability can arise either
through cooling or heating of the emulsion. The strong temperature dependence is char-
acteristic for sterically stabilized emulsions and it separates them from the electrostati-
cally stabilized ones, which are relatively insensitive to the temperature conditions. /15/
The mean emulsion droplet size of a stabilized system is determined by the balance be-
tween droplet breakup and the coalescence. Under shear forces, the interfacial forces
are insufficient to balance the viscous forces leading to the droplets bursting. This can
be compensated by the adsorption of surfactant if it is used. The surfactant adsorption

lowers the interfacial tension between emulsion oil droplets and stabilizer. This reduc-
tion leads to decreasing of the stress needed to deform or break emulsion droplets.
Changes in emulsion rheology, in interfacial elasticity, caused by transport of surfactant